The present invention relates to a developer sheet which is useful in providing visible images through reaction with a color precursor and which is useful in providing transparencies or in providing reproductions having a glossy finish. It more particularly relates to a developer sheet which is capable of providing a controlled degree of gloss ranging from matte to high gloss.
The developer sheet of the present invention can be used in conjunction with conventional pressure-sensitive copy paper or photosensitive imaging systems employing microcapsules to provide visible images upon contact with a color precursor which is image-wise released from the microcapsules and transferred to the developing sheet.
Pressure-sensitive copy paper is well known in the art. It is described in U.S. Pat. Nos. 2,550,466; 2,712,507; 2,730,456; 3,016,308; 3,170,809; 3,455,721; 3,466,184; 3,672,935; 3,955,025; and 3,981,523.
Photosensitive imaging systems employing microencapsulated radiation sensitive compositions are the subject of commonly assigned U.S. Pat. Nos. 4,399,209 and 4,416,966 to The Mead Corporation as well as copending U.S. Pat. application Ser. No. 320,643 filed Jan. 18, 1982. These imaging systems are characterized in that an imaging sheet including a layer of microcapsules containing a photosensitive composition in the internal phase is image-wise exposed to actinic radiation. In the most typical embodiments, the photosensitive composition is a photopolymerizable composition including a polyethylenically unsaturated compound and a photoinitiator and is encapsulated with a color precursor. Exposure image-wise hardens the internal phase of the microcapsules. Following exposure, the imaging sheet is subjected to an uniform rupturing force by passing the sheet through the nip between a pair of pressure rollers.
U.S. Pat. No. 4,399,209 discloses a transfer system in which the imaging sheet is assembled with a developer sheet prior to being subjected to the rupturing force. Upon passing through the pressure rollers in contact with the developer sheet, the microcapsules rupture and image-wise release the internal phase whereupon the color former migrates to the developer sheet where it reacts with a dry developer and forms a color image. The imaging system can be designed to reproduce monochromatic or polychromatic full color images.
Commonly assigned U.S. Pat. No. 4,578,339 discloses oil-containing microcapsules on the imaging sheet and/or the developer sheet. The function of the dyeless microcapsules is to release an oil which mixes with the internal phase released from the photosensitive microcapsules to reduce its viscosity and thereby increase the mobility of the chromogenic material. As a result, the interaction between the developer material and the chromogenic material on the developer sheet is improved. While the reference discloses numerous examples of color developers, they are not all useful in the present invention because they are not necessarily designed to film out upon the application of heat.
In those applications in which the aforementioned pressure-sensitive and photosensitive imaging systems are used to reproduce graphic or picture images, a high degree of gloss is often desired in the reproduction. In particular, where a transparency is desired, the reproduction must transmit light effectively. These objectives are difficult to achieve using conventional approaches. Because the reaction between the developer and the color former occurs principally at the surface of the developer, finely divided developers such as resin grinds are the developer of choice because they provide a large reactive surface area to react with the color former and provide high optical density. However, these compositions usually contain fine dispersing agents or pigments which scatter light and make the image appear dull.
One technique which has been used previously to produce high gloss images is described in U.S. Pat. No. 4,554,235. There, the developer layer is overcoated with a discontinuous layer of a thermoplastic polymeric pigment. After exposure, the imaging sheet is assembled with the developer sheet and subjected to pressure. The color former is released from the microcapsules, passes through the layer of polymeric pigment, and reacts with the developer. Thereafter, the thermoplastic pigment is subjected to heat and/or pressure which causes the pigment to coalesce into a transparent continuous thin film which imparts a glossy finish to the image.